Fluidized bed combustion method for burning wastes

Abstract

A fluidized bed combustion method for burning wastes using a fluidized bed furnace is not affected by a fluctuation in the quantity and quality of wastes fed into the furnace, if any, thereby preventing CO gas, etc. from discharging out of the furnace. The furnace has a number of air-diffusing tubes for feeding primary air to the fluidized bed in parallel with each other at the bottom of the fluidized bed, and a free space part formed above the fluidized bed for burning unburnt matter with a secondary air. Each air-diffusing tube has a number of nozzles provided along the axis of the tube and a primary air control device including an open-close damper for controlling the quantity of air to be fed through the tube. The primary air is fed into the fluidized bed through the air-diffusing tubes one after another according to a predetermined open-close pattern by the primary air control device so that the ratio of the air quantity Uo to the minimum fluidizing air quantity Umf (Uo/Umf) is in the range of 1.4 to 4 when the damper is opened and in the range of 0.5 to 2 when the damper is closed. The dampers are opened and closed at intervals of 1 to 10 seconds, preferably 2 to 10 seconds, and 10 to 100 seconds, respectively.

What is claimed is: 
     
       1. A fluidized bed combustion method for burning wastes using a fluidized bed furnace having a fluidized bed, a number of air-diffusing tubes of feeding a primary air to the fluidized bed arranged in parallel with each other at the bottom of the fluidized bed, and a free space part formed above the fluidized bed for burning unburnt matter with a secondary air, each said airdiffusing tube having a number of nozzles provided along the axis of the tube and a primary air control means including an open-close damper for controlling the quantity of air to be fed, which method comprises feeding said primary air into the fluidized bed through said air-diffusing tubes one after another according to a predetermined open-close control pattern by means of said primary air control means to burn the wastes so that the ratio of the air quantity Uo to the minimum fluidizing air quantity Umf (Uo/Umf) is in the range of 1.4 to 4 when said damper is opened and in the range of 0.5 to 2 when said damper is closed, the dampers being opened and closed at intervals of 1 to 10 seconds and 10 to 100 seconds, respectively. 
     
     
       2. A fluidized bed combustion method for burning wastes according to claim 1, wherein the temperature of the fluidized bed is controlled to fall within a range of 550° to 800° C. by adding an auxiliary fuel or water into the fluidized bed. 
     
     
       3. A fluidized bed combustion method for burning wastes according to claim 1, wherein said secondary air is fed along a flow direction of combustion gas at at least two points in said free space part. 
     
     
       4. A fluidized bed combustion method for burning wastes according to claim 1, wherein the wastes are burned in a circular form furnace and said primary air is introduced at at least two points in the circumferential direction of the wall of said furnace so as to form a whirling flow. 
     
     
       5. A fluidized bed combustion method for burning wastes according to claim 1, further including mixing combustion gas with the secondary air at a secondary combustion zone in the furnace. 
     
     
       6. A fluidized bed combustion method for burning wastes according to claim 5, wherein said mixing includes providing a grating just above the inlet of a secondary air of the furnace. 
     
     
       7. A fluidized bed combustion method for burning wastes according to claim 5, wherein said mixing includes providing a plurality of hollow tubes or rods horizontally penetrating through the secondary combustion zone of the furnace. 
     
     
       8. A fluidized bed combustion method for burning wastes according to claim 7, including providing said hollow tubes with secondary air-spouting nozzles at an under part thereof. 
     
     
       9. A fluidized bed combustion method for burning wastes according to claim 5, wherein said mixing includes providing a plurality of rows of tubes extending laterally on one side of the secondary combustion zone of the furnace and arranged alternately in the flow direction of the combustion gas to that the combustion gas flows in a zigzag path divided by the rows of tubes. 
     
     
       10. A fluidized bed combustion method for burning wastes according to claim 1, wherein said feeding of said primary air into the fluidized bed to said air-diffusing tubes one after another in the predetermined open-close control pattern includes closing the open-close damper of a present air-diffusing tube after an open interval of 5 seconds elapses and substantially simultaneously opening the open-close damper of a next air-diffusing tube to start an open interval of 5 seconds for the open-close damper of the next air-diffusing tube and thereafter repeating the opening and closing for each of the open-close dampers. 
     
     
       11. A fluidized bed combustion method for burning wastes according to claim 10, wherein said feeding of said primary air further comprises feeding said primary air into the fluidized bed through seven air-diffusing tubs one after another so that the open interval of 5 seconds of reach said open-close dampers results in a corresponding closed interval of 30 seconds, said open and closed intervals being repeated sequentially for each of the open-close dampers. 
     
     
       12. A fluidized bed combustion method for burning wastes according to claim 1, wherein said feeding of said primary air into the fluidized bed through said air-diffusing tubes one after another according to the predetermined open-close control pattern includes sequentially opening the open-close damper of a next air-diffusing tube after one half of the open interval of the open-close damper for a present air-diffusing tube has elapsed so that both of the open-close dampers for the present and next air-diffusing tubes are open for one half of the open interval. 
     
     
       13. A fluidized bed combustion method for burning wastes according to claim 12, wherein said feeding of said primary air through said air-diffusing tubes includes providing an open interval for each of the open-close dampers of 10 seconds. 
     
     
       14. A fluidized bed combustion method for burning wastes according to claim 13, wherein said feeding of said primary air through said air-diffusing tubes includes providing seven air-diffusing tubes so that the open interval for each said open-close damper is 10 seconds and the corresponding closed interval is 25 seconds.